一个选项类型，总是 Some 或 None，取决于静态类型参数。

示例

use static_option::*;

enum Inner<Selector: StaticOptionSelector> {
    A(StaticOption<Selector, i32>),
    B(StaticOption<Selector, u32>),
}

enum MaybeInitialised {
    Initialised(Inner<StaticOptionSome>),
    Uninitialised(Inner<StaticOptionNone>),
}